人口密度计算

Question

嗨，伙计们，我正在尝试计算地区的密度和时间短，任何线索我的方法有什么问题？  我使用区域中的最高人口来着色结果，但它在前三个数组$ key =＆gt; $值中给出了空值，最初我使用了数据库中的结果总数，但结果完全错误。< / p>

   $totalDistricts  =count($districts);

            $totalPop=0;

            $maxArr=array();

            // get max value in the  districts data['Total_'] field

            foreach ($districts as &$key)
            {
                $maxArr[]=(int)$key['Total_'];
                // var_dump($key['Total_']);
            }

            $totalPop=max($maxArr);
            // print($totalPop.'  '. $totalDistricts); exit();

            // split the totalPop variable into percentage based ranges
            $ranges         =array
            (
                array((int)floor($totalPop*0.8),$totalPop-1),
                array((int)floor($totalPop*0.5),(int)floor($totalPop*0.8)-1),
                array((int)floor($totalPop*0.2),(int)floor($totalPop*0.5)-1),
                array(0,floor($totalPop*0.2)-1),
            );

            // var_dump($ranges); exit();


            $rankings   =array(array(),array(),array(),array());
            $sorted     =array();
            for ($i=0; $i<$totalDistricts; $i++)
            {
                $sorted[$i]=$districts[$i]['Total_'];
            }
            sort($sorted);

            // a rankings array to group the data based on
            // the total_ column if the total falls within the range, 
            // put them into the matching key=>val range
                   //I have figured part of the problem out, it lies in the foreach loop, the $districts[$key]<- part is wrong

            foreach ($sorted as $key=>$val)
            {
                if ($key>=$ranges[0][0] && $key<=$ranges[0][1])
                {
                    $rankings[0][]=$districts[$key];
                }
                if ($key>=$ranges[1][0] && $key<=$ranges[1][1])
                {
                    $rankings[1][]=$districts[$key];
                }
                if ($key>=$ranges[2][0] && $key<=$ranges[2][1])
                {
                    $rankings[2][]=$districts[$key];
                }
                if ($key>=$ranges[3][0] && $key<=$ranges[3][1])
                {
                    $rankings[3][]=$districts[$key];
                }
            }

这给了我排名数组中的前三个值为空数组，任何线索我做错了什么？